1. Field of the Invention
The present invention relates to an electronic device, a display device and a production method thereof and specifically to a defect repair method for repairing a defective pixel of a liquid crystal display device.
2. Description of the Prior Art
The active matrix-driven liquid crystal display device has a switching element, such as a thin film transistor (hereinafter, referred to as “TFT”), or the like, in each pixel, which is the minimum unit of an image, and is therefore capable of surely lighting each pixel. Thus, the active matrix-driven liquid crystal display device is capable of fine moving-picture display and has been used as various types of displays.
In general liquid crystal display devices developed in recent years, various attempts have been made for the purpose of improving the aperture ratio of a pixel. Especially, a wire is formed of a low-resistance material to make the wire thinner, and the characteristics of a TFT are improved to promote miniaturization of the TFT.
Along with the miniaturization of wires and TFTs, there has been an increasing possibility of a defect in a pixel, which can be caused by wire disconnection, short-circuit, deterioration in the characteristics of TFTs, or the like, due to particles (contaminant particulates), dust, etc., attached onto a substrate surface during the production process of the liquid crystal display device.
In view of such, there have conventionally been proposed techniques of repairing the pixel defect, and the techniques have been practically used in liquid crystal display devices.
For example, Japanese Unexamined Patent Publication No. 7-104311 discloses a liquid crystal display device wherein a plurality of TFTs are provided in each pixel.
FIG. 33 is a schematic plan view of an active matrix substrate 60 of a liquid crystal display device disclosed in Japanese Unexamined Patent Publication No. 7-104311. FIG. 34 is a schematic cross-sectional view of the substrate 60 taken along line XXXIV—XXXIV of FIG. 33. FIG. 35 is a schematic cross-sectional view of the substrate 60 taken along line XXXV—XXXV of FIG. 33.
This liquid crystal display device includes the active matrix substrate 60 which includes a plurality of pixel electrodes 8 arranged in a matrix, a counter substrate which includes a common electrode, and a liquid crystal layer interposed between the substrates.
In the active matrix substrate 60, a plurality of gate lines 1 and a plurality of source lines 2 extend over a glass substrate 10 so as to cross each other at right angles, and capacitor lines 3 run between the gate lines 1 so as to extend in parallel to the gate lines 1. A region enclosed by a pair of gate lines 1 and source lines 2 has a pixel electrode 8. On the gate line 1, a first TFT 5a and a second TFT 5b are provided.
The first TFT 5a includes: a gate electrode which is formed by a part of the gate line 1; a gate insulation film 12 provided so as to cover the gate electrode; a semiconductor film 4 provided on the gate insulation film 12 so as to correspond to the gate electrode; a source electrode provided on the semiconductor film 4, which is a branch of the source line 2; and a drain electrode 19a provided on the semiconductor film 4 and connected to the pixel electrode 8. The drain electrode 19a has a disconnection portion X which has a constricted shape so as to be readily disconnected.
The second TFT 5b has substantially the same structure as that of the first TFT 5a except for a portion between a drain electrode 19b and the pixel electrode 8.
In the portion between the drain electrode 19b and the pixel electrode 8, a drain electrode-extended electrode 19d is provided. The drain electrode-extended electrode 19d is connected to the second TFT drain electrode 19b through a contact hole 19c formed in the gate insulation film 12. An overlapping portion of the drain electrode-extended electrode 19d and the pixel electrode 8 constitutes a connection portion Y.
In this liquid crystal display device, in the process of displaying an image, a gate signal is transmitted through a predetermined gate line 1 so that a first TFT 5a connected to the gate line 1 is turned on. At the same time, a source signal is transmitted through a source line 2 so that a predetermined charge is written in the pixel electrode 8 through the source electrode and the drain electrode 19a. As a result, a potential difference occurs between the pixel electrode 8 and the common electrode, so that a predetermined voltage is applied to the liquid crystal capacitor, which is formed by the liquid crystal layer, and auxiliary capacitor. The applied voltage changes the orientation of liquid crystal molecules which constitute the liquid crystal layer, whereby the transmittance of light coming from the outside is adjusted to display an image.
In the case where any of the pixels is a defective pixel due to the characteristic deterioration of the first TFT 5a, the defective pixel is repaired by irradiating the disconnection portion X of the first TFT 5a with laser light to disconnect the drain electrode 19a and irradiating the connection portion Y with laser light to form a contact hole in the gate insulation film 12 such that a short circuit is caused between the pixel electrode 8 and the drain electrode 19b of the second TFT 5b through the drain electrode-extended electrode 19d. 
As a result, the pixel electrode 8 of the defective pixel is not driven by the first TFT 5a having deteriorated characteristics but by the second TFT 5b. 
However, there is a possibility of a short circuit between the pixel electrode 8 and the drain electrode-extended electrode 19d, i.e., between the conductive layers sandwiching the gate insulation film 12 in which a contact is formed, because the thickness of the gate insulation film 12 is generally as thin as 100 nm to 300 nm such that desirable TFT characteristics are obtained and further because of miniaturization of wires and TFTs in the above-described liquid crystal display device. In other words, when the second TFT 5b is provided in each pixel as a spare, there is a possibility that the fraction defective of the liquid crystal display device increases, and the production yield decreases, contrary to the intent.